Transformer construction



L. E. FEATHER TRANSFORMER CONSTRUCTION Sept. 16, 1969 Original FiledJune 24, 1965 2 Sheets-Sheet l INVENTOR Lundis E. Feather WITNESSES 2iiORNEY Sept. 16, 1969 L. E. FEATHER TRANSFORMER CONSTRUCTION OriginalFiled June 24, 1965 FIG-2- PRI R AR 2 Sheets-Sheet 2 FIG.4-

United States Patent TRANSFORMER CONSTRUCTION Landis E. Feather, Sharon,Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., acorporation of Pennsylvania Continuation of application Ser. No.466,787, June 24,

1965. This application July 28, 1967, Ser. No. 656,947 Int. Cl. H011327/30 US. Cl. 336197 4 Claims ABSTRACT OF DISCLOSURE A transformer ofthe core-form type having a nonmetallic pressure ring formed of aplurality of continuous turns of filamentary fibrous materialimpregnated with a bonding resin. The fibrous material forms 70 to 85%of the weight of the pressure ring. The resin bonding material is epoxyand the fibrous material, glass, is under a tension of 2 to 3 pounds.The ring is between pressure means and the winding and has a flexuralstrength of approximately 100,000 pounds for square inch.

This application is a continuation of application Ser. No. 466,787,filed June 24, 1965, now abandoned.

This invention relates to core-form transformers, and particularly to animproved core-form transformer comprising improved non-metallic pressureplates or rings.

In core-form transformers of the prior art the coils or windings areplaced about the legs of a magnetic core. A frame member is usuallyattached to the upper and lower yoke portions of the magnetic core. Ametallic pressure plate or ring is usually placed'against the coils orwindings at both ends of the coils or windings. Jackscrews are attachedto the frames, which are attached to the upper and lower yoke members;these jack-screws are tightened down against the metallic pressureplates or rings to maintain the coils or windings under pressure toprevent movement of the coils or windings under short circuitconditions. The pressure plates or rings are usually made of steel andare from one half inch to an inch or more in thickness and are washershaped and have about the same inside and outside diameter as the coilsor windings to which they are applied.

These prior art steel pressure plates or rings have severaldisadvantages. The steel pressure plates or rings occupy space in thecore openings thus increasing the necessary core dimensions. Insulationfor the full line potential must be placed between the ends of the coilsor windings and the metallic pressure plates or rings. Low voltage leadswhich must pass between the core and the pressure plates or rings mustbe insulated from the pressure plates or rings. Since the pressureplates or rings are usually made by flame cutting from steel plate,sharp points on the edges of the plates or rings serve as points forstarting corona and electrical breakdown.

Furthermore, eddy current losses in the steel pressure plates or ringsincrease with increasing size of the transformer. In very largecore-form power transformer units, these losses are fequently highenough to cause undesirable heating of the pressure plates or ringswhich will damage the transformer.

Accordingly, it is a principal object of this invention to provide animproved core-form transformer wherein the above referred todisadvantages of the prior art transformers are eliminated.

It is a further object of this invention to provide an improvedcore-form transformer wherein nonmetallic pressure plates or rings areprovided between the ends of the coils and the core.

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It is still a further object of this invention to provide an improvedcore-form transformer which incorporates non-metallic pressure plates orrings composed of filaments bound together into a solid mass with asuitable resin.

It is still a further object of this invention to provide an improvedpressure plate or ring for use in core-form transformers.

It is still another object to provide an improved method of making anon-metallic pressure platev opting for use at the ends of the coils ina core-form transformer.

These and other objects of this invention will be apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIGURE 1 is a partial perspective view of a core-form transformerincorporating non-metallic pressure plates as provided by thisinvention;

FIG. 2 is a plan view of a metallic type pressure plate as used in theprior art;

FIG. 3 is a plan view of the new non-metallic pressure plate or ring;

FIG. 4 is a plan view of a mandrel for manufacturing the improvednon-metallic pressure plate or ring;

FIG. 5 is a side view of the mandrel shown in FIG. 4; and

FIG. 6 is a schematic view of the process used for providing the newpressure plates or rings.

Referring to the drawing in detail, FIG. 1 is a partial perspective viewof a core-form transformer utilizing nonmetallic pressure plates orrings. The transformer of FIG. 1 comprises a magnetic core 10 havingthree leg portions 12, 14 and 16, with an upper yoke portion 18 and alower yoke portion 19 connecting the three leg portions to provide aclosed magnetic circuit. The leg portions and the yoke portions of thecore 10 are made up by stacking laminations of grain oriented siliconsteel, having at least one preferred direction of orientation of grainstructure. A coil 20 comprising a low voltage winding and a high voltagewinding is placed on each of the core legs 12, 14 and 16 before theupper yoke portion 18 is placed in position. A pressure plate or ring 22is placed adjacent the lower end and adjacent the upper end of each ofthe coils 20 during the assembly of the transformer. Frame members 24and 26 are clamped to the upper yoke member 18 and to the lower lokemember 19 by means of bolts 28. The frame members 26 and 28 are providedwith jack-bolts 30. The jack-bolts 30 are positioned in such manner thatafter the coils 20 and the pressure plates or rings 22 have beenassembled in position on the legs of the core 10, the jack-bolts 30 areadjusted to apply pressure to the upper and lower pressure plates orrings 22. The jack-bolts 30 are positioned in such manner that at leastfour jack-bolts 30 apply pressure to both the upper and lower pressureplates or rings 22. The pressure plates or rings 22 each have a slotportion 32 provided therein for facilitating bringing out low voltageleads 34 from the windings 20. The low voltage lead 34 is insulated fromthe respective core legs by means of insulators 36. In a transformer ofthe type described it is necessary to provide pressure on the coils 20to prevent movement of the coils under short circuit conditions, whichoccur during short circuit testing of the transformer or which mightoccur after the transformer is placed in operation.

The pressure plates or rings 22 as illustrated in FIG. 1 are made fromnon-metallic material, such as, glass fiber, roving or tape which isbonded with epoxy or polyester resin and the resin is heat cured toprovide a solid rigid mass. The construction of the pressure plates orrings 22 will be described hereinafter.

In prior art transformers of the type illustrated in FIG. 1, it has beenthe practice to use pressure plates or rings made from steel plate.These pressure plates or rings were flame cut from a solid steel plateto the proper dimension. A pressure ring or plate 38 such as used in theprior art devices is illustrated in FIG. 2. With this type of pressurering it was necessary to flame cut a slot 40 from the ring to permitbringing the low voltage lead 34 out from the inside of the coil 20. Itwas also necessary to cut a slot 42 completely across the pressure ring38 to prevent the pressure plate or ring 38 from acting like a shortedturn. With this type of pressure plate or ring it was also necessary toplace full line potential insulation between the end of the coil 20 andthe pressure plate or ring 38. It was also necessary to completelyinsulate the low voltage leads 34 from the pressure ring 38. Often,because the pressure ring 38 was cut from a solid plate by flamecutting, sharp points occurred on the edges of the rings or plates 38which served as points for starting corona and electrical breakdown.Also, because of stray magnetic flux at the ends of the coils the eddycurrent losses were objectionable and caused undesirable heating of thepressure plates or rings 38 which tended to damage the transformer.

The pressure rings or plate 22 are constructed by winding continuousfilament glass fiber, roving or tape 44 onto a mandrel 46 andimpregnating the fiber, during the winding process, with a heat curableresin, such as epoxy or polyester resin. During the winding of thepressure ring or plate 22 the mandrel 46 is rotated at approximately 40revolutions per minute. This speed of rotation applies a tension ofapproximately 2 or 3 pounds per strand to the fiber. After the plate orring 22 has been wound to the proper size, the mandrel 46 on which theplate or ring 22 has been wound is then placed in an oven and the plateor ring 22 is cured at a temperature of approximately 130 C. forapproximately 2 hours, followed by additional curing at 150 C. for 2additional hours. After this curing the plate or ring 22 is removed fromthe mandrel 46.

Pressure plates or rings 22 constructed according to the above processhave been tested for flexure at room temperature. This test was appliedby laying the ring or plate 22 horizontally on four supports spaced 90apart. A load was applied to four points on the top surface of the ringor plate 22 midway between the bottom supports. Plates or rings 22tested in this manner indicated a flexural strength of approximately100,000 pounds per square inch or more. It was found that pressureplates or rings 22 constructed in this manner, in addition to havinggood flexural strength also had good electrical insulating properties.

Typically, a pressure ring or plate constructed as describedhereinbefore contains from 70 to 85% by weight of continuous filamentglass fiber, roving or tape with the balance of the weight consisting ofan epoxy or polyester resin.

FIGS. 4 and 5 illustrate a suitable mandrel for winding the pressurering or plate 22 as provided by this invention. The mandrel 46 of FIGS.4 and 5 comprises two steel plates 48 and 50 which are separated by aring 52, which ring 52 defines the inside diameter of the pressure ringor plate 22. The maximum outside diameter of the pressure ring or plate22 is defined by the maximum dimension of the steel disks 48 and 50. Themandrel of FIGS. 4 and 5 is provided with an aperture or opening 54 formounting the mandrel 46 for rotation during winding of the fiber toprovide the pressure ring or plate 22.

The process for constructing a pressure plate or ring 22 according tothis invention is illustrated in FIG. 6. In FIG. 6 the referencecharacter 54 illustrates a reel of fiber, such as continuous filamentglass fiber, glass roving or glass tape 44. A container 56 contains aresin 55, such as an epoxy or polyester resin. The fiber 44 is drawnthrough the container 56 by rotating the mandrel 46 at approximately 40revolutions per minute. It is emphasized that the fiber 44 and the resin55 must be compatible so that the resin 55 will completely wet the fiber44. As the fiber 44 is drawn from the container 56 excess resin isremoved by wipers 58. After the fiber 44 passes through the wipers 58 itis wound on the mandrel 46 under a tension of approximately 2 or 3pounds per strand until the desired build up of the pressure ring orplate 22 is obtained. After the required build up of the pressure ringor plate 22 is obtained then the pressure ring or plate 22 is cured onthe mandrel 46 by heat, as described hereinbefore, to provide a solidrigid structure in the form of the pressure ring or plate 22. If it isdesired to provide a slot 32 for bringing the low voltage leads out fromthe inside of the coils 20, before the winding process is started aspacer 60 is placed inside the mandrel, as illustrated in FIG. 4, toprovide a slot 32. This spacer may be simply a block of some typefastened in position inside the mandrel to provide the required slot 32as the filament is wound on the mandrel 46.

Alternatively, the slot may be provided by sawing, after the ring isremoved from the mandrel. Such a sawn slot would be smaller than theslot 40 on the steel plate or ring because it would not be necessary toinsulate the low 'voltage leads from the ring or plate.

From the description hereinbefore it is seen that this inventionprovides a pressure plate or ring 22 of insulating material which isvery rigid and strong and which provides an electrical insulator betweenthe ends of the coils 20 and the core 10 and in which eddy currentlosses will not occur, as in the prior art device. It is also seen thatwith the pressure plate or ring 22 as provided by this invention it isnot necessary to provide full line insulation between the end of thecoil 20 and the pressure plate or rings 22.

Pressure plates or rings 22 may be constructed according to thisinvention with dimensions within approximately the following limits,based on the transformers now being built. The inside diameter of theopening in the ring 22 may be 10 to 24 inches; radial width from theinside opening in the pressure plate or ring 22 to the outside diametermay be 3 to 15 inches; thickness of the pressure ring or plate may be /2to 1 /2 inches. However, these approximate dimensions may vary withdifierent ratings of transformers.

The term epoxy resin as used herein is intended to mean a complexepoxide resin comprising a polyether derivative of a polyhydric organiccompound, e.g., polyhydric alcohol or phenols containing at least twophenolic hydroxy groups, said derivatives containing 1, 2 epoxy groups.The ethoxyline resins as defined are disclosed in various places in theart such as in Castan Patent 2,324,- 483 as well as Castan Patent2,444,333, British Patent 518,057 and British Patent 579,698. US.Patents 2,494,- 295, 2,500,600, 2,511,913 and 2,691,007 disclose otherexamples of epoxy resin compositions. Curing of such compositions isreadily accomplished by acidic (e.g., phthalic anhydride, etc.), orstrongly alkaline materials (e.g., diethylene triamine, etc).

The term polyester resin comprises a material comprising the reactionproduct of a polyhydric saturated or unsaturated alcohol and a saturatedor unsaturated polybasic acid either with or without a modifyingunsaturated monomer such as styrene, etc. Specific examples of the basicmaterial are, for instance, diethylene glycol maleate, dipropyleneglycol maleate, diethylene glycol fumarate, etc. Such materials arereadily polymerized by peroxy catalysts such as benzoyl peroxide,tertiary butyl perbenzoate, etc.

From the foregoing, it is seen that the present invention has provided atransformer comprising non-metallic pressure plates or rings whichovercome many of the disadvantages of the steel or magnetic typepressure plates or rings used in the prior art transformers of thistype.

While the present invention has been shown and described in only oneform, it will be obvious to those skilled in the art that it is not solimited, but is susceptible of various changes and modifications withoutdeparting from the spirit thereof.

I claim as my invention:

1. An electrical transformer, comprising:

a magnetic core having leg and yoke portions,

an electrical winding disposed. in inductive relation about a legportion of said magnetic core;

non-metallic pressure rings disposed about said leg portion of themagnetic core, between each axial end of said electrical winding and ayoke portion of said magnetic core; each of said pressure rings having asubstantially ring shape, with a central opening disposed between firstand second substantially flat major opposed surfaces; each of saidpressure rings including a plurality of continuous tensioned turns offilamentary fibrous material impregnated with a resinous bonding means;said resinous bonding means bonding the fibrous material into a coherentsolid mass; said fibrous material providing 70 to 85% of the weight ofsaid pressure rings, with the balance of the weight being provided bysaid resinous bonding means; I

and means applying pressure to said pressure rings to maintain saidelectrical winding under pressure.

References Cited UNITED STATES PATENTS 1,539,670 5/1925 Hendricks336-197 XR 2,175,336 10/1939 Austin 174-179 XR 2,841,636 7/1958 White174-138, 2,977,406 3/1961 Scott 174-177 3,056,706 10/1962 Knoppcl174-177 3,325,584 6/1967 Herzig 174-179 XR LEWIS H. MYERS, PrimaryExaminer T. J. KOZMA, Assistant Examiner

